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排序方式: 共有221条查询结果,搜索用时 46 毫秒
171.
Loss of meiosis in Aspergillus 总被引:2,自引:0,他引:2
If strictly mitotic asexual fungi lack recombination, the conventional view
predicts that they are recent derivatives from older meiotic lineages. We
tested this by inferring phylogenetic relationships among closely related
meiotic and strictly mitotic taxa with Aspergillus conidial (mitotic)
states. Phylogenies were constructed by using DNA sequences from the
mitochondrial small ribosomal subunit, the nuclear ribosomal internal
transcribed spacers, and the nuclear 5.8S ribosomal gene. Over 920 bp of
sequence was analyzed for each taxon. Phylogenetic analysis of both the
mitochondrial and nuclear data sets showed at least four clades that
possess both meiotic and strictly mitotic taxa. These results support the
hypothesis that strictly mitotic lineages arise frequently from more
ancient meiotic lineages with Aspergillus conidial states. Many of the
strictly mitotic species examined retained characters that may be vestiges
of a meiotic state, including the production of sclerotia, sclerotium-like
structures, and hulle cells.
相似文献
172.
CRISPR/Cas9 and TALENs generate heritable mutations for genes involved in small RNA processing of Glycine max and Medicago truncatula
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Shaun J. Curtin Yer Xiong Jean‐Michel Michno Benjamin W. Campbell Adrian O. Stec Tomas Čermák Colby Starker Daniel F. Voytas Andrew L. Eamens Robert M. Stupar 《Plant biotechnology journal》2018,16(6):1125-1137
Processing of double‐stranded RNA precursors into small RNAs is an essential regulator of gene expression in plant development and stress response. Small RNA processing requires the combined activity of a functionally diverse group of molecular components. However, in most of the plant species, there are insufficient mutant resources to functionally characterize each encoding gene. Here, mutations in loci encoding protein machinery involved in small RNA processing in soya bean and Medicago truncatula were generated using the CRISPR/Cas9 and TAL‐effector nuclease (TALEN) mutagenesis platforms. An efficient CRISPR/Cas9 reagent was used to create a bi‐allelic double mutant for the two soya bean paralogous Double‐stranded RNA‐binding2 (GmDrb2a and GmDrb2b) genes. These mutations, along with a CRISPR/Cas9‐generated mutation of the M. truncatula Hua enhancer1 (MtHen1) gene, were determined to be germ‐line transmissible. Furthermore, TALENs were used to generate a mutation within the soya bean Dicer‐like2 gene. CRISPR/Cas9 mutagenesis of the soya bean Dicer‐like3 gene and the GmHen1a gene was observed in the T0 generation, but these mutations failed to transmit to the T1 generation. The irregular transmission of induced mutations and the corresponding transgenes was investigated by whole‐genome sequencing to reveal a spectrum of non‐germ‐line‐targeted mutations and multiple transgene insertion events. Finally, a suite of combinatorial mutant plants were generated by combining the previously reported Gmdcl1a, Gmdcl1b and Gmdcl4b mutants with the Gmdrb2ab double mutant. Altogether, this study demonstrates the synergistic use of different genome engineering platforms to generate a collection of useful mutant plant lines for future study of small RNA processing in legume crops. 相似文献
173.
Decoupling Photocurrent Loss Mechanisms in Photovoltaic Cells Using Complementary Measurements of Exciton Diffusion
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Significant work has been directed at measuring the exciton diffusion length (LD) in organic semiconductors due to its significance in determining the performance of photovoltaic cells. Several techniques have been developed to measure LD, often probing photoluminescence or charge carrier generation. Interestingly, in this study it is shown that when different techniques are compared, both the diffusive behavior of the exciton and active carrier recombination loss pathways can be decoupled. Here, a planar heterojunction device based on the donor–acceptor pairing of boron subphthalocyanine chloride‐C60 is examined using photoluminescence quenching, photovoltage‐, and photocurrent‐based LD measurement techniques. Photovoltage yields the device relevant LD of both active materials as a function of forward bias subject to geminate recombination losses. These values are used to accurately predict the photocurrent as a function of voltage, suggesting geminate recombination is the dominant mechanism responsible for photocurrent loss. By combining these measurements with photocurrent and photoluminescence quenching, the intrinsic LD, as well as the voltage‐dependent charge transfer state dissociation and charge collection efficiencies are quantitatively determined. The results of this work provide a method to decouple all relevant loss pathways during photoconversion, and establish the factors that can limit the performance of excitonic photovoltaic cells. 相似文献
174.
Sayle KL Bentley J Boyle FT Calvert AH Cheng Y Curtin NJ Endicott JA Golding BT Hardcastle IR Jewsbury P Mesguiche V Newell DR Noble ME Parsons RJ Pratt DJ Wang LZ Griffin RJ 《Bioorganic & medicinal chemistry letters》2003,13(18):3079-3082
A series of O(4)-cyclohexylmethyl-5-nitroso-6-aminopyrimidines bearing 2-arylamino substituents was synthesised and evaluated for CDK1 and CDK2 inhibitory activity. Consistent with analogous studies with O(6)-cyclohexylmethylpurines, 2-arylaminopyrimidines with a sulfonamide or carboxamide group at the 4'-position were potent inhibitors, with IC(50) values against CDK2 of 1.1+/-0.3 and 34+/-8 nM, respectively. The crystal structure of the 4'-carboxamide derivative, in complex with phospho-Thr160 CDK2/cyclin A, confirmed the expected binding mode of the inhibitor, and revealed an additional interaction between the carboxamide function and an aspartate residue. 相似文献
175.
Live and let die: regulatory mechanisms in Fas-mediated apoptosis 总被引:30,自引:0,他引:30
Activation of Fas receptor by Fas ligand causes caspase 8 activation and apoptosis in cells and is an important mechanism by which normal tissue homeostasis and function are maintained. Activation of caspase 8 is preceded by the formation of a death-inducing signalling complex (DISC), and a number of redundant mechanisms regulate DISC formation in vivo. Fas receptor is widely expressed in tissues, and dysfunction of the regulatory mechanisms in Fas receptor signalling has been reported in several diseases including autoimmune disease and cancer. This review aims to identify and discuss the various mechanisms employed by cells to alter their sensitivity to Fas-mediated apoptosis by regulating DISC formation. We also discuss a number of defects identified with Fas receptor signalling and the associated pathologies. 相似文献
176.
Curtin ML Garland RB Heyman HR Frey RR Michaelides MR Li J Pease LJ Glaser KB Marcotte PA Davidsen SK 《Bioorganic & medicinal chemistry letters》2002,12(20):2919-2923
A series of succinimide hydroxamic acids was prepared and evaluated in vitro for HDAC inhibition and tumor cell antiproliferation. While the original macrocyclic analogue 6 was quite potent in both assays, several appropriately substituted non-macrocyclic succinimides, such as 23, were equipotent. 相似文献
177.
178.
Purification and characterization of mycobacterial phospholipase A: an activity associated with mycobacterial cutinase
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We describe mycobacterial phospholipase A activity (MPLA) and, using reverse genetics, have associated this activity with putative mycobacterial cutinase. PLAs, which hydrolyze fatty acids on phospholipids, play a significant role in human inflammatory states and disease pathogenesis. In prokaryotes, the recognition of their role in virulence is more recent. Cutinases are serine esterases whose primary substrate is cutin, the waxy exterior layer of plants. Mycobacterium tuberculosis has maintained seven putative cutinases, though it should not encounter cutin; we demonstrate that known cutinases and MPLA cleave phospholipids in a PLA-type manner and also hydrolyze Tween. We analyzed cutinase motifs in mycobacteria and found the motif very prevalent. All mycobacteria tested had MPLA activity. These studies suggest an alternative use for putative cutinases by the M. tuberculosis group that is likely related to MPLA activity and lipid metabolism. 相似文献
179.
Benjamin J. Povinelli Kathleen M. Kokolus Jason W.-L. Eng Christopher W. Dougher Leslie Curtin Maegan L. Capitano Christi T. Sailsbury-Ruf Elizabeth A. Repasky Michael J. Nemeth 《PloS one》2015,10(3)
The production of new blood cells relies on a hierarchical network of hematopoietic stem and progenitor cells (HSPCs). To maintain lifelong hematopoiesis, HSPCs must be protected from ionizing radiation or other cytotoxic agents. For many years, murine models have been a valuable source of information regarding factors that either enhance or reduce the survival of HSPCs after exposure of marrow to ionizing radiation. In a recent series of studies, however, it has become clear that housing-related factors such as the cool room temperature required for laboratory mice can exert a surprising influence on the outcome of experiments. Here we report that the mild, but chronic cold-stress endured by mice housed under these conditions exerts a protective effect on HSPCs after both non-lethal and lethal doses of total body irradiation (TBI). Alleviation of this cold-stress by housing mice at a thermoneutral temperature (30°C) resulted in significantly greater baseline radiosensitivity to a lethal dose of TBI with more HSPCs from mice housed at thermoneutral temperature undergoing apoptosis following non-lethal TBI. Cold-stressed mice have elevated levels of norepinephrine, a key molecule of the sympathetic nervous system that binds to β-adrenergic receptors. We show that blocking this signaling pathway in vivo through use of the β-blocker propanolol completely mitigates the protective effect of cold-stress on HSPC apoptosis. Collectively this study demonstrates that chronic stress endured by the standard housing conditions of laboratory mice increases the resistance of HSPCs to TBI-induced apoptosis through a mechanism that depends upon β-adrenergic signaling. Since β-blockers are commonly prescribed to a wide variety of patients, this information could be important when predicting the clinical impact of HSPC sensitivity to TBI. 相似文献
180.
V L Sylvia C O Joe J O Norman G M Curtin R D Tilley D L Busbee 《The International journal of biochemistry》1989,21(4):347-353
1. DNA polymerase alpha isolated from Norman murine myxosarcoma exhibited two isozyme forms, one with low specific activity and low DNA binding affinity (A1), and one with high specific activity and high DNA binding affinity (A2). 2. DNA polymerase alpha A1, but not A2, showed a significant increase in specific activity after treatment with phosphatidylinositol, ATP and phosphatidylinositol kinase, or with phosphatidylinositol-4-monophosphate. 3. Treatment of DNA polymerase alpha A1 with the phospholipase C hydrolysis product of phosphatidylinositol-4-monophosphate, inositol-1,4-bisphosphate, was sufficient to effect the transient increase in activity of polymerase A1 to a form not chromatographically distinguishable from isozyme form A2. 相似文献